This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 6 |
| 3 | 45 |
| 4 | 382 |
| 5 | 3498 |
| 6 | 33696 |
| 7 | 336549 |
| 8 | 3453750 |
| 9 | 36197694 |
| 10 | 385817700 |
| 11 | 4169274354 |
| 12 | 45573898860 |
| 13 | 503014992340 |
| 14 | 5598239469972 |
| 15 | 62754598454805 |
| 16 | 707899472049702 |
| 17 | 8029846915852662 |
| 18 | 91534356644739300 |
| 19 | 1048036064453687814 |
| 20 | 12047350849047152388 |
| 21 | 138984261578842304268 |